U.S. Pat. No. 4,075,428 describes an apparatus, in a stored program controlled telecommunication station, for generating regulation values according to a given synchronizing method, said values being transmitted to the frequency regulation input of the station oscillator. The known apparatus includes a digital filter and a memory which stores weight factors, each of which is assigned to one of a number of clocks as well as an algorithm for averaging with the aid of the filter and the weight factors, a number of phase differences between pulses from the station oscillator and the clocks. A change of the network synchronizing method is obtained by changing the memory contents.
It is also known, e.g. from a paper No. 132-1 "Transition to a digital telephone network" which was read at the 1976 International Switching Symposium in Kyoto, Japan, to synchronize a digital stored program controlled telecommunication network with the aid of a method suited to the size of the network and the standard of communication, and to change the synchronizing method at certain occasions, e.g. in conjunction with extending the network or improving its standard. Such a synchronizing method change affects the whole network in question and has so far required rather extensive alterations in all the stations of thereof. Even though apparatus according to said U.S. patent are used, a synchronizing method change includes altering the extensive contents in the program memories of the communication network. Such alterations are difficult to carry out without disturbing network operation.